William Jiang

JavaScript,PHP,Node,Perl,LAMP Web Developer – http://williamjxj.com; https://github.com/williamjxj?tab=repositories

Design Patterns

Design Patterns

Here are some information about Software Design Patterns, original from wikipedia, I put here for quick retrieving. Design patterns were originally grouped into the categories:

  1. Creational patterns
  2. structural patterns
  3. behavioral patterns
  4. Concurrency patterns
Creational patterns
Name Description In Design Patterns In Code Complete[17]
Abstract factory Provide an interface for creating families of related or dependent objects without specifying their concrete classes. Yes Yes
Builder Separate the construction of a complex object from its representation allowing the same construction process to create various representations. Yes No
Factory method Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses (dependency injection[18]). Yes Yes
Lazy initialization Tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed. No No
Multiton Ensure a class has only named instances, and provide global point of access to them. No No
Object pool Avoid expensive acquisition and release of resources by recycling objects that are no longer in use. Can be considered a generalisation of connection pool and thread pool patterns. No No
Prototype Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype. Yes No
Resource acquisition is initialization Ensure that resources are properly released by tying them to the lifespan of suitable objects. No No
Singleton Ensure a class has only one instance, and provide a global point of access to it. Yes Yes

Structural patterns
Name Description In Design Patterns In Code Complete[17]
Adapter or Wrapper or Translator. Convert the interface of a class into another interface clients expect. An adapter lets classes work together that could not otherwise because of incompatible interfaces. The enterprise integration pattern equivalent is the translator. Yes Yes
Bridge Decouple an abstraction from its implementation allowing the two to vary independently. Yes Yes
Composite Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly. Yes Yes
Decorator Attach additional responsibilities to an object dynamically keeping the same interface. Decorators provide a flexible alternative to subclassing for extending functionality. Yes Yes
Facade Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use. Yes Yes
Flyweight Use sharing to support large numbers of similar objects efficiently. Yes No
Front Controller The pattern relates to the design of Web applications. It provides a centralized entry point for handling requests. No Yes
Module Group several related elements, such as classes, singletons, methods, globally used, into a single conceptual entity. No No
Proxy Provide a surrogate or placeholder for another object to control access to it. Yes No

Behavioral patterns
Name Description In Design Patterns In Code Complete[17]
Blackboard Generalized observer, which allows multiple readers and writers. Communicates information system-wide. No No
Chain of responsibility Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it. Yes No
Command Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations. Yes No
Interpreter Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language. Yes No
Iterator Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation. Yes Yes
Mediator Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently. Yes No
Memento Without violating encapsulation, capture and externalize an object’s internal state allowing the object to be restored to this state later. Yes No
Null object Avoid null references by providing a default object. No No
Observer or Publish/subscribe Define a one-to-many dependency between objects where a state change in one object results in all its dependents being notified and updated automatically. Yes Yes
Servant Define common functionality for a group of classes No No
Specification Recombinable business logic in a Boolean fashion No No
State Allow an object to alter its behavior when its internal state changes. The object will appear to change its class. Yes No
Strategy Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it. Yes Yes
Template method Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure. Yes Yes
Visitor Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates. Yes No

Concurrency are described using the concepts of
delegation, aggregation, and consultation.

Concurrency patterns
Name Description In POSA2[20]
Active Object Decouples method execution from method invocation that reside in their own thread of control. The goal is to introduce concurrency, by using asynchronous method invocation and a scheduler for handling requests. Yes
Balking Only execute an action on an object when the object is in a particular state. No
Binding properties Combining multiple observers to force properties in different objects to be synchronized or coordinated in some way.[21] No
Double-checked locking Reduce the overhead of acquiring a lock by first testing the locking criterion (the ‘lock hint’) in an unsafe manner; only if that succeeds does the actual lock proceed.

Can be unsafe when implemented in some language/hardware combinations. It can therefore sometimes be considered an anti-pattern.

Event-based asynchronous Addresses problems with the asynchronous pattern that occur in multithreaded programs.[22] No
Guarded suspension Manages operations that require both a lock to be acquired and a precondition to be satisfied before the operation can be executed. No
Lock One thread puts a “lock” on a resource, preventing other threads from accessing or modifying it.[23] No
Messaging design pattern (MDP) Allows the interchange of information (i.e. messages) between components and applications. No
Monitor object An object whose methods are subject to mutual exclusion, thus preventing multiple objects from erroneously trying to use it at the same time. Yes
Reactor A reactor object provides an asynchronous interface to resources that must be handled synchronously. Yes
Read-write lock Allows concurrent read access to an object, but requires exclusive access for write operations. No
Scheduler Explicitly control when threads may execute single-threaded code. No
Thread pool A number of threads are created to perform a number of tasks, which are usually organized in a queue. Typically, there are many more tasks than threads. Can be considered a special case of the object pool pattern. No
Thread-specific storage Static or “global” memory local to a thread. Yes

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